Ultrasonic dishwasher

ABSTRACT

Piezoelectric transducers are attached to the bottom wall of an upwardly open tub of austenitic stainless steel equipped with a valved inlet in a side wall near the bottom wall, a valved outlet in the bottom wall, a removable cover provided with a receptacle for washing compositions, and a vertical row of contacts on the side wall. After the washer cycle is started by pressing a button, the washer is further controlled automatically by the opening or closing of circuits between the contacts and the grounded tub through the rising or receding liquid in the tub. A safety switch on the outer tank wall is kept closed by a permanent magnet as long as the cover is in position, and the receptacle is dropped to release the washing composition upon retraction of a latch by an electromagnet on the outer face of the tub side wall.

United States Patent [191 Thomen 1 Jan. 9, 1973 [54] ULTRASONIC DISHWASHER FORElGN PATENTS OR APPLICATIONS [76] Inventor: Max Thomen, 67 Ruebisbachstrasse, 265,459 3/1950 Switzerland ..l34/57 D 8202 Kloten, Switzerland Primary Examiner-Robert L. Bleutge [22] Fled: 1971 Attorney-Hans Berman Appl. N0.: 171,094

[57] ABSTRACT Piezoelectric transducers are attached to the bottom wall of an upwardly open tub of austenitic stainless steel equipped with a valved inlet in a side wall near the bottom wall, a valved outlet in the bottom wall, a removable cover provided with a receptacle for washing compositions, and a vertical row of contacts on the side wall. After the washer cycle is started by pressing a button, the washer is further controlled automatically by the opening or closing of circuits between the contacts and the grounded tub through the rising or receding liquid in the tub. A safety switch on the outer tank wall is kept closed by a permanent magnet as long as the cover is in position, and the receptacle is dropped to release the washing composition upon retraction of a latch by an electromagnet on the outer face of the tub side wall.

6 Claims, 7 Drawing Figures PATENTEDJAH "9 I973 3. 709.732

SHEET2UF4 Fig.2

ULTRASONIC DISHWASHER This invention relates to washing machines, and particularly to a dishwasher equipped with ultrasonic transducers for agitating the washing liquor in the tub of the dishwasher.

It is common practice to rely on the mechanical action of water jets for dislodging particles of food and other contaminants from the surface of tableware in an automatic dishwasher. Water alone, even when very hot, is not normally effective enough, and strongly alkaline or oxidizing detergents must be dissolved in the water. The strong detergents tend to bleach overglazes and other colored decorations on the tableware, and attack certain types of glass. Moreover, it is necessary to apply hot air to the washed tableware after washing and rinsing in order to dry the same.

It is known to use ultrasonic transducers for agitating liquid cleaning solutions, but the known ultrasonic cleaning devices are not suitable for household use.

The primary object of this invention is the provision of an ultrasonic dishwasher which is practical for household use.

A more specific object is the provision of a domestic dishwasher which need not rely for full cleaning efficiency on aggressive chemicals and makes it unnecessary to provide hot air for drying the washed tableware so as to operate in a cycle much shorter than that of conventional automatic dishwashers.

With these and other objects in view, the invention provides a dishwasher with a tub of stainless steel having an open top which may be closed by a movable cover. Transducers are mounted on the outer face of the tub bottom wall in such a manner that they may impart ultrasonic vibrations to a liquid in the tub. Contact elements are fixedly mounted on the side wall of the tub and vertically spaced from each other. The contact elements are exposed in the tub for electrical contact with the liquid therein, the lowermost contact element being closely adjacent the bottom wall of the tub. A tubular inlet member is mounted on the side wall adjacent the bottom wall with its axis approximately parallel to the bottom wall.

A receptacle is mounted on the cover for movement between a first position in which it is capable of retaining a particulate washing composition and a second position in which the composition is dripped from the receptacle into the tub. A latch arrangement normally retains the receptacle in its first position against the force of gravity, but it may be permitted to move into the second position when the latch arrangement is released by an electromagnet mounted on the outer face of the tub whose field, when energized, includes a movable ferromagnetic latch member.

The afore-mentioned tubular inlet member and a tubular drain member on the bottom wall are opened and closed by electrically operated valves. The valves, the transducers, the latch' releasing magnet, and the contact elements on the side wall are conductively connected to a central control mechanism which operates the transducers, the latch releasing magnet, and the valves in response to electrical contact between the contact elements and the liquid in the tub. A support is provided for holding tableware in a suitable position in the tub.

Other features, additional objects, and many of the attendant advantages of this invention will readily be appreciated as the same is better understood by reference to the following description of a preferred embodiment when considered in connection with the appended drawing in which:

FIG. 1 shows a dishwasher of the invention in front elevational section;

FIG. 2 shows the dishwasher of FIG. 1 built into a kitchen counter, the view being in front elevation;

FIG. 3 is a fragmentary diagram of the electrical circuits in the same dishwasher;

FIG. 4 shows a portion of the tableware support in the dishwasher on a larger scale in elevation and partly in section;

FIG. 5 illustrates the device of FIG. 4 in another operating position; and

FIG. 6 and FIG. 7 show another portion of the tableware support in the manner of FIGS. 4 and 5 respectively.

Referring now to the drawing, and initially to FIG. 1, there is seen the approximately cubical tub I of a dishwasher which is deep drawn from austenitic stainless steel sheet. The open top of the tub is closed by a removable plastic cover 2. The outer face of the bottom wall 3 of the tub I carries a group of adhesively fastened barium titanate transducers 4 arranged in a pattern to uniformly transmit ultrasonic energy to a liquid in the tub when the transducers are energized at about 25,000 CPS. A housing 5 protects the transducers.

In the installed condition of the washer, a hot water line is connected to an inlet tube 6 whose axis is horizontal and thus parallel to the bottom wall 3 and to the tubular upright wall 12 of the tub near the juncture of the upright and bottom walls. A drain tube 7 is provided on the bottom wall 3 and is equipped with a poppet valve 8 which may be opened and closed by two electromagnets 9, l0 oppositely spaced from a common armature member 11 in the direction of pivoting movement of the latter on the drain tube 7, the end portion of the armature member 11 remote from the magnets being hingedly fastened to the stem of the valve 8.

Three contact elements l3, l4, 15 are mounted in a vertical row on the upright wall 12. The lowermost contact element 13 is closely adjacent the bottom wall 3 and barely above the level of the inlet tube 6, and the topmost contact element 15 is just below the cover 2. Each of the elements consists of a plastic insulating plug and a Monel wire passing centrally through the plug so that one of its ends is exposed in the tub I.

The cover 2 carries a permanent magnet 16 which, in the illustrated operative position of the cover 2, is aligned with a switch 17 mounted on the outer face of the tub 1 whose material is non-magnetic. The switch 17 has a fixed contact and a movable contact sealed in a glass envelope. The movable contact is magnetic and resilient so that it is normally biased toward the open position, but closes a circuit when in the field of the magnet 16.

An aperture in the cover 2 is closed in the condition of the apparatus shown in FIG. I by a scoop-shaped receptacle 18 secured to the bottom face of the cover 2 by a hinge 19, the free end of the receptacle being held in the illustrated position against the force of gravity by a latch rod 20 of mild steel biased toward the operative position by a helical compression spring 21. An electromagnet 22 is arranged on the outer face of the upright wall 12 in alignment with the latch rod 20. When the magnet 22 is energized, it attracts the rod against the restraint of the spring 21, and thereby releases the receptacle 18 to drop its contents, such as a surfactant, into the tub I.

As is common practice, the tub I may be installed in a freestanding housing (not shown) mounted on casters, or it may be installed in a kitchen counter in the manner illustrated in FIG. 2 so that its open top is vertically aligned with a corresponding aperture, not visible in the view of FIG. 2, in the counter top 25. The tub is normally hidden in a sink cabinet which may be flush with another cabinet 26 and a kitchen stove 27 as is conventional. A nipple 28 on the bottom of the tub I connects the drain tube 7 with a siphon 29. A mixing faucet 30 arranged above the open top of the tub permits the tub to be used as an ordinary kitchen sink if desired. A panel 31 conceals the ultrasonic generator that energizes the transducers 4 and carries the several control knobs 32 to 38 and a timer 39 for automatic operation of the dishwasher. When the tub is used as a sink, the cover 2 may be stored in a bracket on a wall of the sink cabinet, and the cabinet also provides space for a basket 40 of wire coated with polyvinyl chloride plastisol which supports tableware during the automatic washing cycle.

The control panel 31 obscures not only the aforementioned ultrasonic generator, but also relays and other circuit elements of a control unit 41 (FIG. 3)

which are connected with the drain magnets 9, 10, the contact elements 13, 14, 15, the reed switch 17 and the magnets, not shown, which operate the non-illustrated valve in the inlet tube 6 in the manner illustrated with reference to the valve 8. The tub 1 provides a common ground connection for the several electrical devices mounted thereon, and is connected by a ground lead 42 with the circuit elements on and behind the control panel 31.

The current supply tov the electrically operated elements of the dishwasher is controlled by a contactor operated by the reed switch 17. All current is shut off when the cover 2 is removed. The push button 32 operates the main switch of the machine. The push buttons 33 to 35 permit a fully automatic or semi-automatic washing cycle to be selected or a mode of operation in which a load is washed only, but not dried. The push buttons 36, 37 are arranged in series with the contact elements 14, 15 so that they may inactivate one of the two contact elements but only one. The button 38 when depressed, starts a selected washing program.

The timer 39 may be set to determine the period during which the non-illustrated high-frequency generator energizes the transducers 4.

The circuitry of the control unit 41, not shown in detail, is controlled by a drum switch operated by means of a small synchronous motor as is customary in automatic washing machine. In operating the machine, when loaded with dishes to be washed, the cover 2 is closed first to operate the safety switch 17. One of the buttons 33 to 35 is pushed to set the desired program, the main switch is closed by pushing the button 32, and the desired water level during washing is set by pushing one of the buttons 36, 37. The period of ultrasonic button 38 for automatic operation, the valve 8 is closed, the non-illustrated valve in the inlet tube 6 is opened, and the magnet 22 is energized briefly to dump a particulate surfactant from the receptacle 18 into the whirling water discharged from the tube 6. When a circuit is closed between the lowermost contact element 13 and the tub 1, the non-illustrated high-frequency generator is energized. As the water level reaches the contact element 14 or 15 which has remained active, the water flow from the tube 6 is shut off, and the timer 39 is started. It may be set to open the drain valve 8 30 seconds to 6 minutes after the desired maximum level is reached, and the ultrasonic generator is shut off as the descending water level passes the lowermost contact element 13. Opening of the circuit through the element 13 also causes the inlet tube 6 to be opened briefly after a delay of approximately 5 seconds to flush debris from the bottom of the tub 1 into the drain tube 7. 20 seconds later, the valve 8 is shut automatically, the inlet tube 6 is opened and the second period of the cycle, similar to the first period, is started. if it is desired to use a surfactant in the second period also, the receptacle 18 may be returned manually to the illustrated position and again charged with washing composition at any time during the first period.

When the second period approaches its end, the inlet tube 6 is not opened again, and the valve 8 remains open as long as current is supplied to the machine. The cover 2 may then be removed, and the washed dishes withdrawn.

The surfactant employed has the dual function of facilitating the release of gas bubbles, more specifically air bubbles, from the liquid in the tub, and of dispersing or emulsifying the soil particles dislodged from the tableware by cavitation under the influence of ultrasonic oscillations in the liquid after the air bubbles are released. Because the ultrasonic treatment is continued while the washing liquid is discharged through the drain tube 7, the surfactant-bearing liquid is drained completely from the tableware in the basket 40 if the pieces of tableware are positioned so as not to trap water. The oscillation during draining also prevents redisposition of soil on the tableware, particularly in the second period of the cycle. The tableware, when properly set in the basket 40, is withdrawn dry and clean from the tub I.

Mild, non-foaming surfactants and emulsifiers are adequate for operation of the illustrated dishwasher since they are not needed for releasing soil from the tableware. Such surfactants are staple articles of commerce and do not affect overglaze or sensitive glass. The washing cycle in fully automatic operation takes only about 10 to 15 minutes since it does not include the hot-air drying period of conventional dishwashers.

When the button 34 is pressed to set the washing program, the second period is omitted. The drain valve 8 remains open after the first washing period. This is sufficient for lightly soiled tableware. When the button 35 is pushed, the ultrasonic generator is shut off by the timer 39 while the valve 8 remains closed and the liquid level in the tub I is maintained at its maximum value set by the button 36 or 37. This mode of operation may be selected for cleaning heavily soiled kitchen utensils for which the last-described individual cycle may precede a normal automatic cycle, or when it is desired to add more tableware after a first washing.

The armature member 11 is preferably mounted on the drain tube 7 with sufficient friction to maintain its angular position when the magnets 9, are deenergized. The valve 8 is thus opened or closed by a brief electrical pulse transmitted from the control unit 41 to the magnets 9, 10 respectively, and remains open or closed thereafter. The valve 8 is held closed by the pressure of the liquid in the tub I, but it is preferred that the magnet 10 receive pulses repeated from time to time as long as the valve 8 is desired to remain open.

The only movable mechanical elements in the illustrated dishwasher are the valves in the inlet and drain tubes, and the receptacle 18. Additional movable elements are provided in the basket 40 for effective cleaning of tumblers or other cup-shaped pieces of tableware as is shown in FIGS. 4 to 7.

Referring initially to FIGS. 4 and 5, there is seen a support member 45 which is a normally stationary element of the basket 40. Two open-meshed wire grids 46 respectively act as carriers for two tumblers 50. One end of each grid 46 is pivotally attached to the support member 45 for movement through an angle determined by two abutments 47, 48. The other end of each grid is provided with entegral hooks 49 which retain the corresponding tumbler 50 in a fixed position relative to the grid 46. The far end of the grid also carries a tube 51 whose ends are sealed and which is filled with air to act as a float.

When the tub I is empty of water, the grids 46 engage the lower abutments 47 whereby the open ends of the tumblers 50 are directed downwardly. When the tub I is filled with water to its operating level, the floats 51 raise the grids 46 so that the tumblers 50 are open in a direction which has an upward component.

During washing, the tumblers 50 are thus held in the position seen in FIG. 5 in which no gas can be trapped within the tumblers, and the liquid wets all internal and external tumbler surfaces and exposes them to the action of the ultrasonic oscillation. When the water level drops, the tumblers are drained as they move toward the position shown in FIG. 4. Because the ultrasonic oscillations continue during most of the draining period, no droplets of water are left behind on the glass surfaces to stain the same after drying.

A correspondingly operating portion of the basket 40 suitable for carrying coffee or tea cups provided with a handle is shown in FIGS. 6 and 7.

A member 52 of the basket 40 pivotally supports a carrier frame 53 equipped with hooks 54 from which cups 55 are suspended by their handles. The hooks 54 cooperate with transverse members 56 of the frame 53, which act as stops for the cups 55, to maintain a fixed position of the cups on the carrier frame 53. A float 57, different from the afore-described float 51 in its dimensions only, pivots the carrier frame 53 and the cups suspended therefrom from the position of FIG. 6 to that of FIG. 7 as the liquid level in the tub l rises, while abutments 47, 48 on the supporting member 52 limit the angle of pivoting movement between the two terminal positions illustrated in which the cups are open downwardly for draining liquid or upwardly for release of gas, as described with reference to the tumblers 50 in FIGS. 4 and 5.

It should be understood, of course, that the foregoing disclosure relates only to a preferred embodiment of the invention, and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.

What is claimed is:

l. A dishwasher comprising:

a. a stainless steel tub having an upright side wall, a bottom wall, and an open top opposite said bottom wall;

. a cover movable toward and away from an operative position in which said cover, closes the open top of said tub;

c. transducer means mounted on the outer face of said bottom wall for imparting ultrasonic vibrations to a liquid in said tub;

. a plurality of contact elements fixedly mounted on said side wall and vertically spaced from each other,

I. said contact elements being exposed in said tub for electrical contact with said liquid,

2. the lowermost of said contact elements being closely adjacent said bottom wall;

e. a tubular inlet member mounted on said side wall adjacent said bottom wall and having an axis approximately parallel to said bottom wall;

f. a receptacle mounted on said cover for movement between a first position in which said receptacle is capable of retaining a particulate washing composition and a second position in which said composition is dropped from said receptacle into said tub;

g. latch means for retaining said receptacle in said first position against the force of gravity;

h. electrically operated latch releasing means for releasing said latch means and for thereby permitting said receptacle to move into said second position thereof,

1. said latch releasing means including an electromagnet mounted on an outer face of said tub, and

2. said latch means including a ferromagnetic latch member arranged on said cover for movement in the field of said electromagnet when said electromagnet is energized;

(i). a tubular drain member on said bottom wall;

(j). electrically operated valve means in each of said tubular members for opening and closing the associated tubular member;

(k). control means conductively connected to said transducer means, to said contact elements, to said latch releasing means, and to said valve means for operating said transducer means, said latch releasing means, and said valve means in response to conductive contact between said liquid and said contact elements in timed sequence; and

I. support means for holding tableware in a predetermined position in said tub.

2. A dishwasher as set forth in claim 1, wherein one of said valve means includes a valve member movable between an opening position and a closing position, an armature member secured to said valve member for simultaneous movement, and two electromagnets oppositely spaced from said armature member in the direction of movement of the armature member and conductively connected to said control means.

3. A dishwasher as set forth in claim 1, further comprising selector switch means in circuit with two contact elements upwardly spaced from said lowermost contact element for selectively inactivating said two contact elements respectively.

4. A dishwasher as set forth in claim 1, wherein said control means include a switch mounted on an outer face of said tub and including a ferromagnetic contact member movable between a circuit closing and a circuit opening position and yieldably biased toward one of said positions thereof, said cover carrying a permanent magnet, said magnet attracting said movable contact member and holding the same in the other member between a first position in which said cupshaped piece is upwardly open and a second position in which said cup-shaped piece is downwardly open, and operating means responsive to a change in the level of liquid in said tub for moving said carrier between said positions thereof.

6. A dishwasher as set forth in claim 5, wherein said carrier includes a wire frame pivotally secured to said support member for pivotal movement between said positions thereof, and said operating means include a float attached to said carrier. 

1. A dishwasher comprising: a. a stainless steel tub having an upright side wall, a bottom wall, and an open top opposite said bottom wall; b. a cover movable toward and away from an operative position in which said cover closes the open top of said tub; c. transducer means mounted on the outer face of said bottom wall for imparting ultrasonic vibrations to a liquid in said tub; d. a plurality of contact elements fixedly mounted on said side wall and vertically spaced from each other,
 1. said contact elements being exposed in said tub for electrical contact with said liquid,
 2. the lowermost of said contact elements being closely adjacent said bottom wall; e. a tubular inlet member mounted on said side wall adjacent said bottom wall and having an axis approximately parallel to said bottom wall; f. a receptacle mounted on said cover for movement between a first position in which said receptacle is capable of retaining a particulate washing composition and a second position in which said composition is dropped from said receptacle into said tub; g. latch means for retaining said receptacle in said first position against the force of gravity; h. electrically operated latch releasing means for releasing said latch means and for thereby permitting said receptacle to move into said second position thereof,
 1. said latch releasing means including an electromagnet mounted on an outer face of said tub, and
 2. said latch means including a ferromagnetic latch member arranged on said cover for movement in the field of said electromagnet when said electromagnet is energized; (i). a tubular drain member on said bottom wall; (j). electrically operated valve means in each of said tubular members for opening and closing the associated tubular member; (k). control means conductively connected to said transducer means, to said contact elements, to said latch releasing means, and to said valve means for operating said transducer means, said latch releasing means, and said valve means in response to conductive contact between said liquid and said contact elements in timed sequence; and
 1. support means for holding tableware in a predetermined position in said tub.
 2. the lowermost of said contact elements being closely adjacent said bottom wall; e. a tubular inlet member mounted on said side wall adjacent said bottom wall and having an axis approximately parallel to said bottom wall; f. a receptacle mounted on said cover for movement between a first position in which said receptacle is capable of retaining a particulate washing composition and a second position in which said composition is dropped from said receptacle into said tub; g. latch means for retaining said receptacle in said first position against the force of gravity; h. electrically operated latch releasing means for releasing said latch means and for thereby permitting said receptacle to move into said second position thereof,
 2. said latch means including a ferromagnetic latch member arranged on said cover for movement in the field of said electromagnet when said electromagnet is energized; (i). a tubular drain member on said bottom wall; (j). electrically operated valve means in each of said tubular members for opening and closing the associated tubular member; (k). control means conductively connected to said transducer means, to said contact elements, to said latch releasing means, and to said valve means for operating said transducer means, said latch releasing means, and said valve means in response to conductive contact between said liquid and said contact elements in timed sequence; and
 2. A dishwasher as set forth in claim 1, wherein one of said valve means includes a valve member movable between an opening position and a closing position, an armature member secured to said valve member for simultaneous movement, and two electromagnets oppositely spaced from said armature member in the direction of movement of the armature member and conductively connected to said control means.
 3. A dishwasher as set forth in claim 1, further comprising selector switch means in circuit with two contact elements upwardly spaced from said lowermost contact element for selectively inactivating said two contact elements respectively.
 4. A dishwasher as set forth in claim 1, wherein said control means include a switch mounted on an outer face of said tub and including a ferromagnetic contact member movable between a circuit closing and a circuit opening position and yieldably biased toward one of said positions thereof, said cover carrying a permanent magnet, said magnet attracting said movable contact member and holding the same in the other position thereof when said cover is in the operating position.
 5. A dishwasher as set forth in claim 1, wherein said support means include a support member, a carrier adapted to fixedly hold a cup-shaped piece of tableware, said carrier being movable on said support member between a first position in which said cup-shaped piece is upwardly open and a second position in which said cup-shaped piece is downwardly open, and operating means responsive to a change in the level of liquid in said tub for moving said carrier between said positions thereof.
 6. A dishwasher as set forth in claim 5, wherein said carrier includes a wire frame pivotally secured to said support member for pivotal movement between said positions thereof, and said operating means include a float attached to said carrier. 